Various liquid dispensing systems use air assisted extrusion nozzles to apply viscous material, such as thermoplastic material, onto a moving substrate. Often times, these systems are used to form nonwoven products. For example, meltblowing systems may be used during the manufacture of products such as diapers, feminine hygiene products and the like. In general, meltblowing systems include a source of liquid thermoplastic material, a source of pressurized process air, and a manifold for distributing the liquid material and process air. A plurality of modules or dispensing valves may be mounted to the manifold for receiving the liquid and process air and dispensing an elongated filament of the liquid material which is attenuated and drawn down by the air before being randomly applied onto the substrate. In general, a meltblowing die tip or nozzle includes a plurality of liquid discharge orifices arranged in a row and a slot on each side of the row of liquid discharge orifices for dispensing the air. Instead of slots, it is also well known to use two rows of air discharge orifices parallel to the row of liquid discharge orifices.
Controlled fiberization dispensing systems also use air assisted extrusion nozzles. However, the pressurized process air in these systems is used to swirl the extruded liquid filament. Conventional swirl nozzles or die tips typically have a central liquid discharge passage surrounded by a plurality of process air discharge passages. The liquid discharge passage is centrally located on a protrusion. A common configuration for the protrusion is conical or frustoconical with the liquid discharge passage opening at the apex. The process air discharge passages are typically disposed at the base of the protrusion. The process air discharge passages are usually arranged in a radially symmetric pattern about the central liquid discharge passage. The process air discharge passages are directed in a generally tangential manner relative to the liquid discharge orifice and are all angled in a clockwise or counterclockwise direction around the central liquid discharge passage.
Another type of air assisted nozzle, referred to herein as a bi-radial nozzle, includes a wedge-shaped member having a pair of side surfaces converging to an apex. A liquid discharge passage extends along an axis through the wedge-shaped member and through the apex. The wedge-shaped member extends in a radially asymmetrical manner around the liquid discharge passage. Four process air discharge passages are positioned at the base of the wedge-shaped member. At least one process air discharge passage is positioned adjacent to each of the side surfaces and each of the process air discharge passages is angled in a compound manner generally toward the liquid discharge passage and offset from the axis of the liquid discharge passage.
These and other types of air-assisted extrusion nozzles generally require periodic maintenance due to accumulation of dust, hardened liquid material, or other reasons. Each dispensing valve may have to be unbolted from the manifold by unscrewing at least two bolts. The nozzle is then removed from the dispensing valve and another nozzle is mounted onto the valve. If necessary, the valve is reattached to the manifold. Consequently, such repair can increase the required shut down time for removal and replacement of valves and nozzles. Removal of the entire dispensing valve with the attached nozzle is generally a requirement when changing between applications (e.g., meltblowing to controlled fiberization).
For these reasons, it is desirable to provide apparatus and methods for quickly changing nozzles on a die assembly without encountering various problems of prior liquid dispensing systems. It is also desirable to provide for easier maintenance and replacement of air-assisted extrusion nozzles.